This invention concerns television receivers and is particularly directed to systems in which the television image is projected on a viewing screen greater in area than the screen of the conventional console television receiver.
The size of the imaging screen of the cathode ray tube is limited to a practical maximum of about 25 inches (diagonal measure). While cathode ray tubes as large as 35 inches in diagonal measure have appeared in consumer products, the tube envelope becomes so big and unwieldy that any benefit resulting from the increase in screen size is offset by the great increase in cost, size and weight. In addition, brightness and resolution fall off rapidly with relatively small increments of increase in screen size much beyond 25 inches.
As a result, attempts to provide increased screen sizes have been directed mainly to projection systems. In many kinds of projection television systems, the television image is formed on the cathodoluminescent screens of a plurality of monochrome color cathode ray tubes providing discrete red, green and blue images, for example, and the images are combined and focused on a remotely located viewing screen by an arrangement of lenses and mirrors. Viewing screen sizes are typically in the range of 40 to 72 inches in diagonal measure.
The simplest type of projection television system is one in which the image on the screen of a television receiver, usually of the small-screen type, is magnified by a simple projection lens embodied in a housing that shields the screen. The enlarged image is normally projected onto a reflecting screen, although the image may as well be directed towards a rear-projection screen that forms a part of the housing. The brightness of the projected image is enhanced by increasing the intensity of the image on the receiver screen by electronic means, and by using a directional screen.
Three other basic projection system configurations have appeared in the market place. One is a two-piece system comprising a free-standing projection unit physically separated from a remotely located viewing screen. One commercially available model of this type has a screen of 72 inches in diagonal measure, and has a projection distance of more than eight feet.
Another basic configuration is a system in which a forwardly tilted, curvilinear viewing screen, which may be demountable, is mounted uprightly at the back of a cabinet. The optical assembly, which commonly includes three projection cathode ray tubes and associated focusing lenses, is housed in the cabinet. The optical assembly casts a plurality of images on a mirror which, in preparation for operation, is transported on slide means forwardly away from the screen toward the viewer to a fixed position. The purpose is to reflect the images on the screen where they are brought into coincidence, thus providing the necessary projection distance. The larger the viewing screen, the longer the projection optical path and the closer to the viewer the mirror must extend. In one product of this type, for example, wherein the viewing screen is 60 inches in diagonal measure, the mirror is transported nearly two feet toward the viewer from the cabinet proper. An example of a system of this type is disclosed in U.S. Pat. No. 4,058,837 to Muntz.
A third type is a "rear-projection" system in which the image is projected on the rear of the viewing screen for viewing by an observer located at the front of the screen. An example is the Model PR4800SW manufactured by Quasar Electronics Corp., Franklin Park, Illinois. The system is contained in a single large cabinet the height of a tall china cabinet. The screen is exposed for viewing by opening the doors of the upper section of the cabinet to reveal a screen of 45-inch diagonal measure. Another example of a television set with a fixed rear projection screen is disclosed in U.S. Pat. No. 4,177,484 to Boje.
A very early television set developed by Zenith Radio Corporation (circa 1939) comprised a long cathode ray tube having a screen diagonal measure of about eleven inches mounted vertically in a cabinet. The image on the screen was viewed indirectly by means of a mirror mounted on the under-side of the hinged cabinet lid, with the lid oriented at a convenient angle for viewing.
Projecting television receivers of the large-screen types described, despite the obvious benefit of larger viewing screens, have not received the widespread acceptance accorded the conventional large-screen console television set which commonly has the twenty-five inch screen that is relatively small in area when compared to projection system screens. The massiveness and the extensive floor space required have made most projection systems generally unattractive to the average homeowner who is more used to contemporary home furnishings of the compact type. In addition, the overall incompatability of many projection receivers with such furnishings is accentuated by factors such as an awkward configuration, especially when a system such as a two-piece projection system, is set up for operation. Further, the need in most cases to set up the receiver is not appealing to the homeowner used to pressing a single button to activate his familiar console television set.